The human nervous system senses current information and conditions. It sends instructions to various muscles to respond. Neuromuscular disorders can disrupt this information exchange and lead to undesired muscle responses.
As one example, consider the facial and neck nerves. These motor nerves control the muscles of facial expression and, thus, an individual's outward manifestations of well being and emotion.
Dystonias, the involuntary contraction of facial or neck muscle, can distort the individual facial expressions and garble the outward appearance of an individual's feeling of well being and emotional state. For example, one type of dystonia, called blepharospasm, creates uncontrolled blinking and spasms in the eyelids. Another form of dystonia causes uncontrolled grimacing. Dystonias can also affect neck muscles, too. For example, a form of dystonia, called torticollis, causes uncontrolled contraction of the neck muscles.
Apart from these hyperfunctional disorders, normal contraction of facial and neck muscles, e.g. by frowning or squinting, can over time form permanent furrows or bands in the skin. These furrows or bands can present an aesthetically unpleasing cosmetic appearance. Exposure of the skin to the sun can accelerate this undesired wrinkling process.
As a more specific example, the facial muscle Corrugator supercilii draws the eyebrows downward and inward, producing vertical wrinkles of the forehead, also called glabellar frown lines. For this reason, Corrugator supercilii is known as the "frowning muscle" and has been called the principal agent in the expression of suffering.
Dystonias affecting the Corrugator supercilii can lead to an unfortunate, continuous frowning expression. It can also lead to the formation of hyperfunctional frown lines and wrinkles in the face, which have an adverse cosmetic effects.
A surgical forehead lift procedure is one therapeutic modality to remove glabellar frown lines. The forehead lift entails a large incision that extends from ear to ear over the top of the forehead. This surgically invasive procedure imposes the risk of bleeding and creates a large skin flap that reduces blood supply to the skin. Numbness of sensory nerves in the face, like the supraorbital nerve, can also result.
Another, less surgically invasive therapeutic modality is the administration of invertebrate exotoxins in a pharmaceutically safe form. For example, serotype A of the Botulinum toxin, when injected into the Corrugator supercilii, produces a flaccid paralysis of the muscle (see, e.g., The New England Journal of Medicine, 324:1186-1194. 1991). Tests have demonstrated that Botulinum toxin A may be administered into the musculature of the face without toxic effect to produce localized relation of muscle for a period of time, e.g., about six months (Blitzer, et al., Otolaryngol Head and Neck Surg., 119:1018-1023, 1993).
The desired removal of hyperfunctional frowning lines is temporary. Repeated treatments are required.
In a related area, U.S. Pat. No. 5,714,468 reports the periodic injection of invertebrate neurotoxin, such as Botulinum toxin A, into facial muscles to reduce the pain associated with migraine headache.
Keller U.S. Pat. No. 5,370,642 employs laser energy to eliminate glabellar frown lines and forehead wrinkles. The laser energy causes large scale resection of the corrugator and other facial muscles to inactivate them. Like the surgical forehead lift, numbness of supraorbital nerve and other sensory nerves in the face can result.